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Science News has a story of strange bedfellows. It seems that Antarctica was once adjacent to what is now the American Southwest, some 800 million years ago. Earth's continents then formed a supercontinent called Rodinia, predating Pangaea by some 550 million years. "...the ratios of neodymium isotopes in the ancient sediments in the Transantarctic Mountains are the same as those in what was then Laurentia, says Goodge. Also, the hafnium isotope ratios in the 1.44-billion-year-old zircons found in East Antarctica match those of the zircons found in the distinctive granites now found primarily in North America. Finally, the researchers note, the ratios of various isotopes and elements in a basketball-sized chunk of granite found in East Antarctica — a chunk ripped by a glacier from bedrock now smothered by thick ice, the team speculates — match those of granite found only in what was southwestern Laurentia, which today is the American Southwest."

Good point. My understanding about the theoretical pre-history of continents only went as far back as Gondwana, which dates back roughly 500 million years and is a very different map to the one in TFA, so I had a look at this [wikipedia.org] to refresh my memory and try to resolve conflicts. If TFA is true, then the continents really do shift pretty quickly and change direction a fair bit too, considering Australia started in the northern hemisphere according to TFA, went South to join Gondwana and is now heading North again.

But back to your point about how they knew what it was called, I have a related question. How do they know that Eastern Laurentia had crinkle cut coastlines like Canada? Weren't they formed by glacial activity? How does that happen at the equator?

Also, it wasn't clear to me from TFA whether the magnetic field lines conflict with this theory or support it. If they do conflict, how do we know that the distribution of isotopes isn't due to some other phenomenon?

No. Nothing on the surface remains from those days. There are literally billions of years between the formation of moon and the first continent we know anything of. Even if earth would have been inhabited by advanced (non-spacefaring) civilizations in the meantime, we wouldn't know. There is simply nothing that remains.

There are geological features remaining with a age over three billion years. It's not enough, though, to make out the total plate structure or anything. A native advanced civilization should have left fossile remains of related species. "Visitors" is naturally another thing.

I thought the current theory was that Gondwana the resulting scar of whatever hit the earth forming the moon such a very long time ago. How many generations super continents where there?

Oh wow, that's so not-even-wrong that it goes beyond being not-even-wrong to being not-even-wrong. It's achieved stasis in the continuum of wrongness. (Sorry - I'm watching Dr Who - claptrap overload.)

The giant impact that is the best working explanation for the formation of the Moon (and parallel hypotheses for the formatio

But back to your point about how they knew what it was called, I have a related question. How do they know that Eastern Laurentia had crinkle cut coastlines like Canada? Weren't they formed by glacial activity? How does that happen at the equator?

Most likely, they don't know that, or even think that it did. Continental drift maps are usually drawn by moving around the outlines of the modern continents for the most part, probably because that best communicates which parts went where, rather than amorphous blobs labeled things like "p.s. this is actually Canada".

My understanding would be that the actual outline of the old continents looked nothing like that and we have no way to figure out what they actually did look like.

I happened to catch part of a program on the History Channel this morning that was talking about Rodinia and how the coalition of the continents into a supercontinent disrupted ocean currents, allowing the poles to become colder, expanding the continuously-frozen area until the process ran away, completely covering the Earth in ice until the eruptions that accompanied the breakup of the supercontinent threw CO2 and methane into the air that couldn't be absorbed into the oceans (covered as they were by ice), building up to the point where the greenhouse effect melted a permanent ice-free zone, which (being darker than the ice) would absorb more heat, triggering a positive feedback. The program described this happening in a single freeze-and-thaw, although some 'snowball earth' theories suggest that there were several freezovers as the CO2/methane levels rose and fell until the Cambrian Explosion. It seemed to me, though, that the arguments for Rodinia and Snowball Earth can also be explained by other theories, and that drawing conclusions about conditions that far in the past based on evidence that can accumulate in different ways is going to remain somewhat speculative.

Why do all discussions of Rodinia talk about a single super-continent? How do we know that there was only ONE super-continent on one side and the rest was H2O? couldn't there have been 2 or 3 other landmasses that are now at the bottom of the ocean or even melted back into the earth core by now?

"My understanding would be that the actual outline of the old continents looked nothing like that and we have no way to figure out what they actually did look like."

Why so black and white? Just because we don't know every detail does not mean we have no way to figure out how the earths crust has changed over time. What you are missing is that to a large degree the continents sit in the middle of tectonic plates while the edges of the plates move over and under each other, coastline can change dramatically with the level of the oceans but this has nothing to do with the movement of plates or the location of the continent. Where continents do sit meet the edge of the plates you get mountain ranges. These together with ocean trenches mark the edges of ancient/modern collisions and seperations. Add evidence from fossils, the current motion of the plates, geological features, etc, and it gives you a resonable idea (ie: not a precise map) of what bits have moved where over time. The only thing that I know of where the gross features would be impossible to reconstruct are the land masses that have been subsumed back into the mantle, AFAIK this occurs mainly in deep ocean trenches and not in the middle of a continental land mass (eg: The bedrock in central Australia is ~4 billion years old, The Hawaian islands are an example of a long lived volcano in the middle of a plate).

BTW: Tropical glaciers still exist today but only at very high altitudes.

"Continental drift maps are usually drawn by moving around the outlines of the modern continents for the most part"

actually, no, what is primarily used is geological core examination, where they look at all the layers of rock, at the atomic decay of various isotopes, etc, etc, the idea came from someone looking at the continents, and saying it looks like Africa and south America fit together like a jigsaw piece. just the appearance alone, wasn't enough to 'scientifically' prove or date when areas were piec

But back to your point about how they knew what it was called, I have a related question. How do they know that Eastern Laurentia had crinkle cut coastlines like Canada? Weren't they formed by glacial activity? How does that happen at the equator?

Most likely, they don't know that, or even think that it did. Continental drift maps are usually drawn by moving around the outlines of the modern continents for the most part, probably because that best communicates which parts went where, rather than amorphous blobs labeled things like "p.s. this is actually Canada".

My understanding would be that the actual outline of the old continents looked nothing like that and we have no way to figure out what they actually did look like.

Actually, it seems to be quite a bit more complicated than just moving things around to see where they match. David Morgan-Mar had a nice rundown of one case as an annotation in irregular webcomic here [irregularwebcomic.net] (He must be really bored sometimes).

In this case, two separate places have geological and biological features that match despite being on opposite sides of the atlantic ocean, so you can well guess those features existed before separating.

But back to your point about how they knew what it was called, I have a related question. How do they know that Eastern Laurentia had crinkle cut coastlines like Canada? Weren't they formed by glacial activity? How does that happen at the equator?

The coastlines on the maps are the more or less modern coastlines, superimposed on the ancient plates, purely to help orient us. I think they assume we don't take the coastlines literally.

There are lots of interesting sites with graphics of continental drift

***I have a related question. How do they know that Eastern Laurentia had crinkle cut coastlines like Canada? Weren't they formed by glacial activity? How does that happen at the equator?***

As others have pointed out, the maps tend to be drawn with modern features in place to help with orientation and recognition. In point of fact, the East Coast of Laurentia probably didn't exist until 600-700 million years ago (evidence about the exact date is a bit contradictory) when one of the fractures in Rodinia separated Laurentia from Gondwanaland by opening up an ocean called the Iapetus Sea. The Iapetus subsequently closed in a complicated series of events starting about 460 million years ago and then opened up again on a sort of parallel line in the Triassic forming the modern Atlantic. We (think) we know where the East coast of Laurentia was because there is a quite distinctive geologic boundary called Emmon's (Logan's) Line that can be traced from Newfoundland to Georgia where Iapetus sea sediments were pushed up into/onto Laurentia as the Iapetus Sea closed. There are a couple of zigs and zags in Emmons line -- one NW of New York city and one SE of Montreal -- but mostly it follows the course of the Appalachian mountains and lies a bit West of the Easternmost range of the mountains.

How do they know that Eastern Laurentia had crinkle cut coastlines like Canada? Weren't they formed by glacial activity? How does that happen at the equator?

They also show a gap for the Gulf of Mexico [wikipedia.org], which isn't supposed to exist for another few hundred million years, in the Late Triassic [wikipedia.org]. Almost all of the Pangea maps (including the one at the Smithsonian Museum of Natural History) I have seen do this too. Maybe I am just confused about something.

If that doesn't get your head spinning with conspiracies, start thinking about how much was probably destroyed through action or negligence over the centuries. You also have to consider much of this was not found or understood until recently. What will we find about the past in the next 100 ye

IIRC it's not all that odd at all. Russians are allowed to have a few scientists going around naming things if they want. Wikipedia (which may be my original source) agrees with me: "In geology, Rodinia (from the Russian [rodina], or 'motherland')..."

Go spring or fall... crank up the Harley and pack some doob... bring a camera... stuff your ugly bitch in the seat behind you... and stay at Panamint Springs (the other places are run by contractors with federal NPS contracts).

There is NOBODY there. It's a space as big as Connecticut and you have it all to yourself and maybe a few dozen other people. After a few days you start to recognize them; you even start waving at each other when you pass. It's totally like Antarctica.

I have been to Death Valley many times and have seen very few harleys, so don't let the though of them keep you from a very cool place. Like anywhere people go (fortunately), they always clump up in a few places, leaving everywhere else empty. Leave the beaten path by only 100 yards and you will have it to yourself.

Revving your goddamn engine at a stop sign to make your dick sound bigger (0 mph) is, I concede, a safe speed for neighborhood driving. It still wakes up my kid, and any driver who can't see a stationary douchebag on a motorcycle isn't going to take noise into consideration.

Besides, if being noticed is a problem, why is the standard-issue biker uniform an oh-so-visible black?

If you really want to be seen, you should get a giant orange flag installed, or a flashing light on the end of a pole like the cops do. Motorcycle cops have no trouble being seen without making environmentally dubious modifications to their machines. You should be able to, also.

In a world where bikes cost more than many cars, no one is on a bike because it's "all they can afford." Your right to ride a death-mobile through a neighborhood doesn't trump the kids' right to go to school rested enough to learn

Motorcycle cops have no trouble being seen without making environmentally dubious modifications to their machines.

I know, changing the restriction or path of the exhaust just before it goes into the atmosphere by swapping or removing the muffler just causes the emissions on those things to skyrocket! Goddamn polluters!

I couldn't think of any motorcycles with catalytic converters when I wrote the GP post, but I thought there must be some...but after your comment I did a search and turned up nothing, which makes sense when you consider that motorcycles have maybe 2~3 feet of pipe between the collector and the muffler, almost all of which is exposed. Do you know of any motorcycles with catalytic converters?

Normal pipes are loud enough. Bikes with sound and emissions control devices removed are simply inconsiderate. If you think that that is necessary to ride safely, perhaps you should consider... owning a small car instead. You'll even get better gas mileage.

Most bikers that die in accidents weren't wearing proper protective gear (i.e. helmets. and "skull caps" aren't helmets, at least, not from a safety standpoint.) There is very little correlation between muffler removal and accident avoidance.

If you think that people are driving by sound, your kidding yourself. If people were, you would just be making it MORE dangerous for the guy that doesn't act like an ass, because his normal sounding bike would sound farther away than your mating call model.

The oldest one proposed is called Columbia, existing from 1.8 - 1.5 bya.The next widely accepted was Rodinia, existing from 1.3 bya - 800 myaThe next possible was Pannotia, but it didn't last long, only from 600 - 550 mya.The last one was Pangaea, from 250 mya to 150 mya.

The earliest ones are deduced mainly from paleomagnetism, so there may have been earlier supercontinents that we do not know about due to a lack of rocks that old.

Thanks, that's very helpful. Last I heard, the age of the earth was estimated to be around 4.5 billion years, so that leaves a lot of time before Columbia. Does it make any sense to speak in terms of continents back then? When did the oceans start to form?

Wikipedia talks about Vaalbara, Ur and Kenorland predating Columbia, which was then followed by Rodinia, Pannotia, Pangaea, Laurasia and Gondwana.

This was all unknown to me until about ten minutes ago, but I'm pleased to see the Pilbara region of Australia (my country) is one of the oldest places on Earth, stretching back 3.6 billion years (the other's in South Africa).

I guess that if you can date the geology, you can talk about the continents, but their shape must be a bit of a mystery.

I thought I read once that Antarctica was considered a desert because its precipitation levels were so low. (the snow doesn't melt, therefore it doesn't go through the water cycle and precipitate!) Or maybe that was the Arctic. Or Siberia. Hmm.

Lack of life is the term that I heard most, not actual precipitation levels, in college. The Alaskan Tundra, for example, is also considered a desert by some people/political groups/environmentalists. The poles and a few other areas are considered deserts by some. As a side note: It wasn't until about five years ago that I learned that there was a rain forest in Alaska.

What type? Biologists... The "correct" term is meteorological and refers to the precipitation while biologist's use it to refer to the conditions themselves regardless of the weather. (Oh, and pretty crappy professors really but I majored in drinking and minored in failing so it worked out well enough.)

I thought I read once that Antarctica was considered a desert because its precipitation levels were so low.

Correct. It's too cold for liquid water to form and evaporate into the atmosphere, so the air is dry and it does not rain. The definition of "arid" is less than 50mm of rain per year (I believe). As it doesn't rain, it is a desert. The definition is not connected to the degree of life present (deserts have life), nor by high temperatures.

It doesn't make any sense to my layman ears that super-continents could just randomly form when continental plates are drifting about aimlessly. Analogously, that's like the novice bouncing ball program with all balls occasionally striking the same point simultaneously.

I have a practical joke that relates to this article. While I was in Antarctica [gdargaud.net] 15 years ago, one of the geologists was planning a field trip and telling us what he planned/hoped on finding, even showing us some types of rocks. The chopper pilots were scheduled to go near his field area before on an unrelated mission, so they took a large 'interesting' rock out of his accumulated stash and put it in a very visible flat area.

A few days later, the first thing the geologist sees when he reaches the area is of course this rock. He aborts his trip, comes back to the main base all excited about some revolutionary theory or other and starts writing feverishly about it. It took us a bit of courage to tell him the truth and deflate him... He was able to go back to his advanced camp, but it proves that it can be too easy to fake/mistake data in some cases.

Wow, this was indeed a cruel and a funny joke at the same time. Also, it is one of the most expensive practical jokes I've heard of.

However, I am sure that once he analyzed it he would have realized that something was wrong, because the rock did not match the specs of a rock that existed in that environment, on the surface, for some time.

Eventually the genius of the joke would have been spotted; unless of course he would be too excited about it and ended up selecting only the data that fits his model, etc.

A better questions is: You mean they don't? WTF, somebody call Mr Brin! This is a serious oversight. I've been hankerin' to trawl me through some archeology street views, I want to see those humans that lived with dinosaurs.

Just because you confuse "theory" (argument supported by facts) and "hypothesis" (educated guess) doesn't mean that other people are wrong and that people who do science are talking out their asses.

This is exactly like the retard^W Creationist argument that "I've never seen any animal evolve into another species" totally ignoring what is actually/meant/ by the accepted definition of "species" while the retard^W Creationist uses his own private definition of "species".

Sorry - you've just brought to mind a quote from 'Brassed Off'. Mr Chuckles the clown is entertaining a group of kids in a church hall, but he's just about had enough. He comes out with:

So God was creating man. And his little assistant came up to him and he said: "Hey, we've got all these bodies left, but we're right out of brains, we're right out of hearts and we're right out of vocal chords." And God said: "Fuck it! Sew 'em up anyway. Smack smiles on the faces and make them talk out of their arses." And

Sure, all science is theory. However, some science is very robust and some is highly speculative so saying "all science is just theory" is very misleading.

Newtonian physics etc is very robust until you deal with very small particles or very high speeds. Einstein's stuff helps extend that. Same deal with electricity. Most of this has been fairly stable for many years.

Paleontology, climatology and geomorphology are all a lot more speculative and we can expect many of these theories to continue to change fairl

umm the point of science is to change as new knowledge is discovered. That is in direct contrast to dogma's generally non-changing ways. (even though it has anyway due to scientific discoveries)
Also your statement "All science is theory" is being used incorrect. You see the scientific use of the word "theory" is the same as the word "fact." To be classified as a theory, the hypotheses has to be put through rigorous tests that attempts to disprove it have failed.
What you are thinking of is "hypotheses" w

Has anyone noticed that the continents are all still connected? If you take the water out of the oceans, there is dirt there. It's not like continents are big rafts or something, when they hit each other, mountains or trenches form, they don't just float around...

Actually, the continents are different from the sea floors, and not just because of the water. They do in fact "float around like rafts" over the sea floors, creating new sea floor behind them and pushing it down below them in front into trenches. The sea floors are much younger than land surfaces for that reason.